1. Field of the Invention
The present invention relates to electronic chip components used as chip resonant elements and band-pass filters. More specifically, the present invention relates to a electronic chip component including a chip provided with a resonator electrode and input and output electrodes connected or coupled to the resonator electrode.
2. Description of the Related Art
Various types of band-pass filters used in high-frequency regions, such as dual-mode band-pass filters and band-pass filters using a wavelength resonator, have been proposed.
For example, Patent Document 1, Japanese Unexamined Patent Application Publication No. 2001-237610, discloses a dual-mode band-pass filter using a resonator electrode including a through hole. As shown in the cross-sectional view and a schematic plan view in FIGS. 15A and 15B, a dual-mode band-pass filter 101 includes a dielectric substrate 102. A resonator electrode 103 is disposed at the center in a height direction of the dielectric substrate 102. The resonator electrode 103 includes a through hole 103a. The resonator electrode 103 generates a plurality of resonance modes which are not degraded. The through hole 103a couples the resonance modes, such that the dual-mode band-pass filter is obtained.
Ground electrodes 104 and 105, which face the resonator electrode 103, are disposed on the upper and lower surfaces of the dielectric substrate 102. Also, as shown in FIG. 15B, input/output coupled electrodes 106 and 107 are coupled to the resonator electrode 103. Although not shown in FIG. 15A, the input/output coupled electrodes 106 and 107 extend outward from the vicinity of the resonator electrode 103 and are electrically connected to input/output electrodes (not shown).
In a chip-shaped band-pass filter in which ground electrodes are disposed over and under a resonator electrode via dielectric substrate layers, such as the dual-mode band-pass filter 101, or in a band-pass filter in which a ground electrode covers four surfaces of a substrate, the ground electrode is usually also provided on side surfaces of the dielectric substrate. Therefore, the ground electrodes define a waveguide. In other words, the resonator electrode 103 is in the waveguide. With this configuration, resonance is generated depending only on the shape of the waveguide. On the other hand, the above-described waveguide portion defined by the ground electrodes is inevitably larger than the resonator electrode 103.
With this configuration, a basic-mode resonance caused by the ground electrodes is generated at the side of a frequency lower than the resonance frequency of the resonator electrode 103, and higher modes thereof tend to be generated one after another at the portion overlapping the resonance mode of the resonator electrode 103. The resonance caused by the ground electrodes generates undesired spurious signals in the dual-mode band-pass filter 101, and thus a favorable transmission characteristic is not obtained.